Four days. 80,000 fans, 150 musical acts, including giants Pearl Jam and Dead and Company (featuring members of the Grateful Dead and John Mayer).

It's strange to think that over 14 years, Bonnaroo has become an annual event that Manchester, Tenn., could set its watch to. But as the town prepares for the 15th annual festival, it seems like a fitting time to turn back the clock — to June 20, 2002.

That was the day "Bonnaroo" became a household name among Middle Tennesseans. But it wasn’t because of the music. It was because no one could get to work on time.

On the eve of the first Bonnaroo, Interstate 24 effectively became a parking lot for nearly 30 miles, as cars and campers waited for hours to file into the grounds of Great Stage Park.

Traffic planners weren’t the only people that Bonnaroo caught by surprise with its success. In 2002 putting on a massive music and camping festival was seen as bucking the trend — tempting fate, even. It was just three years after Woodstock ’99, which descended into rioting, arson and reports of sexual assaults. To many, producing another large-scale event like that was a dangerous proposition.

Bonnaroo’s producers had a different perspective. They took inspiration from annual events held by “jam band” rockers Phish, as well as European festivals that had run successfully for decades. They booked Phish frontman Trey Anastasio and dozens of other like-minded acts, and hoped that those bands' grassroots fanbases would spread the word.

It worked. Bonnaroo sold 60,000 festival passes in 19 days, before they’d spent a cent on advertising. As Anastasio closed the festival on its final day, he was one of many marveling at what they’d accomplished.

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Bonnaroo arrived in 2002 with a traffic jam for the ages on I-24.(Photo: George Walker IV / File / The Tennessean)

"While the world is thinking that good, positive gatherings of people in the form of live music is something that's going the way of the wind, I actually feel quite the opposite," he said on stage. "I mean, look at this ... the fact that media and people are not noticing, maybe that's a good thing.”

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Of course Bonnaroo’s success didn’t go unnoticed for long. Fourteen years later, it’s one of dozens of multi-day, outdoor music festivals that spring up in the U.S. every year.

And these days, Bonnaroo's musical identity is tougher to pin down, as its lineup aims to appeal to everyone, not just jam-band fans. You'll see big names from the worlds of rock , rap and roots music.

And you'll see many of those performers on the lineups of other festivals — 2016 headliners LCD Soundsystem, for example, are also performing at this year’s Coachella and Lollapalooza. Still, Bonnaroo co-founder Rick Farman believes the festival continues to set itself apart from the pack.

“I still think that Bonnaroo is one of those places that the top acts and emerging acts really feel a need to play,” he said. “We still have more people wanting to the play the festival than we can possibly program. We consider ourselves fortunate in that regard, and sometimes, there's an aspect that's a little easier. Some acts aren't going to Europe (to play festivals) when they were in the past. They can actually stay in America and play a festival season.”

Cata Valencia gets cooled off by Christina Parsons who was hosing people down from the heat at the Bonnaroo Music and Arts Festival on Saturday June 13, 2015, in Manchester.
John Partipilo/The Tennessean

Florence Welch, of Florence and the Machine, performs on the What Stage at the 2015 Bonnaroo Music and Arts Festival on Sunday June 14, 2015 in Manchester, TN.
Gregory French / MTSU Seigenthaler News Service

Jack Landstreet, bottom, and Sam Goldstein, top, exercise on a "Bamboo satellite" at the campgrounds at the Bonnaroo Music and Arts Festival on Sunday June 14, 2015, in Manchester, TN.
John Partipilo / The Tennessean

Savannah Grace, Jacqueline Kolowich and Conner Lentz and Kyle Oreffice of Atlanta rented a U-Haul to camp out in at Bonnaroo Music and Arts Festival on Thursday June 11, 2015.
Shelley Mays/The Tennessean, The Tennessean

Savannah Grace, Jacqueline Kolowich and Conner Lentz and Kyle Oreffice of Atlanta rented a U-Haul to camp out in at Bonnaroo Music and Arts Festival on Thursday June 11, 2015.
Shelley Mays/The Tennessean

Savannah Grace, Jacqueline Kolowich and Conner Lentz and Kyle Oreffice of Atlanta rented a U-Haul to camp out in at Bonnaroo Music and Arts Festival on Thursday June 11, 2015.
Shelley Mays/The Tennessean

Jacob Hemphill, of SOJA, performs Friday at the 2015 Bonnaroo Music and Arts Festival. Jacob Hemphill, of SOJA, performs Friday at the 2015 Bonnaroo Music & Arts Festival in Manchester, TN.
Gregory French MTSU Seigenthaler News Service

Tom MacArthur takes down his totem that was hanging on a geodesic dome that he and other friends rented at the Bonnaroo Music and Arts Festival on Monday June 15, 2015, in Manchester.
John Partipilo / The Tennessean

Jason Collee of Cleveland TN hangs out a little longer in "
The Grove" where he had camped out all week on the last day of the Bonnaroo Music and Arts Festival on Monday June 15, 2015, in Manchester.
John Partipilo / The Tennessean

Even when the acts on the bill don’t set Bonnaroo apart, the people who are buying tickets do.

Almost all of Bonnaroo’s attendees — which reaches 80,000 in sell-out years — make the festival’s campground their home for four days and nights, and are either taking in live music or partying back at their camp at all hours of the day. It's also a pilgrimage, as roughly 85 percent of attendees come to Bonnaroo from outside of Tennessee. Compare that to Lollapalooza, which gets much of its audience from the Chicago area and sends attendees home at 10 p.m. each night.

Bonnaroo's audience, on the other hand, is a captive one — and committed to having a good time. The festival now has an official code for attendees, and one of its key tenets is to "Radiate Positivity" in the form of "smiles, high fives, and random acts of kindness."

That's an ethos that people such as Bryan Blake from Henderson, Ky., have taken to heart. This year will mark his ninth consecutive Bonnaroo.

"As soon as I pull in to the campgrounds, I feel like I have come back to such a warm, familiar place," he said. "I have made many friends that have become like family to me at Roo."

Positivity seems to radiate through Bonnaroo's concert audiences, too. Countless performers have sung the praises of its crowd.It even seemed to get through to the seen-it-all likes of Sir Paul McCartney, who told his 2013 audience, "You are something, Bonnaroo."

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And though carefree vibes permeate the grounds throughout the weekend, Bonnaroo is big business, too, of course. A general admission ticket for this year's fest ran from $324.50 to $349.50, with additional charges for parking, camping and VIP options. For each ticket sold, $3 goes directly to Coffee County. Another $2 goes to the Bonnaroo Works Fund, which has donated $7 million to various arts, education and environmental causes, with a focus on local organizations.

Bonnaroo had a $51 million economic impact in 2012, the last time a study was conducted. That included $36 million in direct local spending. That kind of business eventually attracted Live Nation, which last year purchased a controlling stake in the festival. The massive entertainment company also owns Ticketmaster and controls more than 60 festivals around the world.

The new partnership has already led to new developments on the festival grounds, including the most talked-about addition this year: permanent bathrooms.

Farman is also looking forward to future, unnamed developments on the Bonnaroo property. Even as they celebrate festival No. 15, he says he and his co-founders are keeping their focus on the future, not the past.

"I think all of us personally feel grateful that this thing has been as successful as it has been," he said. "And it's been such a special thing for all of the people who've been a part of it."

Contact Dave Paulson at 615-664-2278 or on Twitter at @ItsDavePaulson.